1. Field of the Invention
The present invention relates to communication networks, and more specifically to a method and apparatus for tracing routes in networks based on broadcast medium (e.g., Ethernet).
2. Related Art
A networking environment generally includes network devices connecting user systems. User systems are used to implement user applications, which provide corresponding features to the users using the end systems. A network device (“hereafter device”) generally refers to a device which forwards data packets (“packets”) between end systems to support various network applications.
It is often helpful to know the specific intermediate devices present in a path taken by packets from a source system (e.g., computer system) to a destination system. For example, when troubleshooting a perceived problem of low data transfer throughput between the source and destination systems, a network administrator may wish to know the intermediate devices so that the problem can potentially be isolated to one of more of the intermediate devices. The path formed by the sequence of the intermediate devices is often referred to as a route between the corresponding source and destination systems.
Utilities which allow the determination of a route (between a source and a destination system) are commonly referred to as trace-route utilities. The well-known “Trace-Route” software program which provides the layer-3 devices between two systems is an example of such an utility. Such an utility generally lists the routers (which operate at the networking layer, also referred as layer-3) present in the path between a source and destination system. Further details of the Trace-Route utility are described in further detail in books entitled, “Internetworking with TCP/IP Volume 1”, by Douglas E. Corner, and “TCP/IP Illustrated Volume 1”, by W. Richard Stevens, which are both incorporated in their entirety herewith.
Unfortunately, the Trace utility operating at layer-3 level typically does not provide information on any layer-2 devices present in the path between a source and a destination system. The feature is particularly problematic in networks based on broadcast medium since the route taken by packets is not generally pre-configured (i.e., not pre-provisioned, for example, as in ATM networks) and the route is generally determined dynamically. A broadcast medium generally refers to a medium in which several devices would generally be capable of receiving a packet intended for even a point-to-point communication. An example environment may be based on Ethernet/802.3 technology as is well known in the relevant arts.
With respect to routes, in Ethernet/802.3 environment well known in the relevant arts, each device determines the specific direction (usually port on the device) a system is in, by examining a source address present in a received packet header. The path may vary if redundancy is present in the network. In addition, a network administrator may not be able to rule out the introduction of additional devices in the network by other persons. Accordingly, a network administrator having responsibility for a network based on broadcast medium may have particular motivation to know the presence of any intermediate layer-2 devices between two end systems.
Thus, what is needed is a method and apparatus which traces the layer-2 route between a source system and destination system.